Patent GB-1282105-A (GB)
Title: Object positioning system and method
IPC: G05B19/18
Filed: 1969-08-14
Abstract: 1282105 Photo-electric apparatus RCA CORPORATION 14 Aug 1969 [21 Aug 1968] 40726/69 Heading G1A [Also in Division H4] Apparatus for adjusting the position of an object with respect to a reference point includes a table for moving the object in two directions; first and second means responsive to movement in the first and second directions respectively, for measuring the respective distances d e , d g , to be moved to make the reference point coincide with first and second indicia on the object; first and second control means moving the table opposite to the first and second directions by the distances d f , d h , to be moved to make the reference point coincide with the indicia when the object is correctly positioned; and a subtractor for forming the error signals d e  -d f  and d g -d h  whereby the table is positioned correctly relative to the reference point. In computer controlled apparatus, Fig.3, for positioning an integrated circuit "chip" accurately on to a board 50 having metal terminals 12a-d, Fig.1, to which the chip is to be bonded, the board 50 is mounted on a table 52 movable in two orthogonal directions. The board is initially aligned on the table by securing tightly against alignment elements e.g. pins or bars. Due to tolerances in the alignment and manufacture of the board the optical fibre 62 in microscope 57, which is fixed relative to the "chip", will be above point 14 which is displaced slightly from the correct position 14a. Light from the light source 54 is reflected downwards by a half-silvered or apertured mirror 58 and the light reflected from the board is focussed by lens 60 on to the end of an optical fibre 62. The other end of the optical fibre is connected to a photo-multiplier 64 and an amplifier 66. The computer 90 adjusts the output 94 of the dark reference level circuit 70 to the level of the amplifier output 96, providing a reference input for the comparator 68. The reference level circuit 70 may be a potentiometer having a wiper driven by a servomotor controlled by the computer, the wiper output being the circuit output 94. The X and Y stepping motors 72, 74 are now actuated and the table is moved such that the fibre 62 is above point 18 on the light coloured metal terminal 12b. The X motor 72 is then actuated to move the table along line 20, the number of steps taken being recorded in X counter 82. When the edge of the terminal is crossed the comparator signals the change in reflected light level to the computer 90. The computer continues stepping for six further steps. If the comparator output remains unchanged for these six steps the motor 72 is stopped. If the comparator output changes back during these six steps the motor continues to step. This procedure avoids errors due to changes in the reflected light level caused by small scratches or imperfections on the board. The distance traversed, d e , is recorded in the computer memory. The table is now moved back along line 20 by an amount d f  equal to the predetermined correct distance that would have been traversed if the point 14 had been in the correct position 14a. The computer now forms the error signal Ex = d e  - d f , taking into account the six extra steps, and stores the result. The process is now repeated to obtain the error in the ydirection, E y . The table is then moved so that the optical fibre element 62 is above point 42 on the second terminal 12c. The processes are repeated to find the errors E x 1 and E y 1 in the position of point 42, these errors are averaged with Ex and E y . If the resulting average errors are small, the table is returned so that the fibre 62 is above point 14. The errors are then allowed for, bringing the fibre to its correct position over point 14a. If the errors are large the other two terminals are also scanned to produce more accurate results. Instead of starting the operation from point in the centre of the terminals, a dark square within a metal frame may be used to position the board as above, Fig.4 (not shown), the size of the square may be used to identify different boards.